Narrative The goal of this proposal is to develop a safe and effective way to prevent the immune response that leads to type I diabetes. Project Summary Type I diabetes (T1D) is an autoimmune disorder in which insulin-producing [unreadable]-cells are destroyed by autoreactive T cells. Once the islets are destroyed they do not readily regenerate, and patients must take replacement insulin to survive. More then 300,000 Americans have T1D, and another 30,000 will be diagnosed this year alone. Several genetic susceptibility markers have been identified for T1D, and antibodies specific for islet antigens can be detected in the blood before severe islet destruction takes place. Despite the improved ability to predict susceptibility to T1D, there is currently no way of stopping the onset of the disease. We intend to change this by developing a new type of vaccine that can be used to teach the immune system not to attack insulin-producing cells. Recently, we developed a new antigen targeting platform that exploits a novel class of non-coding RNAs, known as microRNA. By incorporating target sequences for specific microRNAs into an antigen-encoding gene, we could target expression of the antigen to specific cells types and cell states. Using this technology, we will develop a means to induce and expand islet-protective regulatory T cells (Tregs). Initial studies will be carried out to optimize the microRNA-regulated system to target antigen expression to antigen presenting cells in a manner that will promote the induction of Tregs. Following these studies, we will evaluate the effectives of our approach for preventing T1D in non-obese diabetic (NOD) mice. microRNA-regulated gene vaccines encoding islet antigens will be constructed, and NOD mice will be treated with the vaccines, and monitored for the development of diabetes. By inducing islet-protective Tregs, we expect to subdue the diabetogenic immune response and prevent T1D. This novel platform, which will be the first vaccine to target antigen specifically to tolerogenic cells, will provide a powerful means for preventing T1D in humans.